On asp:Textbox the RadTooltip is correct but not on RadTextbox and RadMaskTextbox

I use :
RadInput.Net2.dll version 2.0.2.0
Prometheus version 2007.1.521.0. 

<form...>

<asp:ScriptManager ID="ScriptManager1" runat="server" />

<div>RadTextBox :<radI:RadTextBox ID="RadTextBox1" runat="server"/></div>

<div>TextBox :<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox></div>

<div>RadNumericTextBox :<radI:RadNumericTextBox ID="RadNumericTextBox1" runat="server">

</radI:RadNumericTextBox> </div>

<asp:Button ID="ButtonNext" runat="server" Text="Suivant" />

<telerik:RadToolTip ID="RadToolTip2" runat="server"

TargetControlID="TextBox1"

Sticky="true"

RelativeTo="Element"

Position="BottomCenter">

<asp:Label ID="Label1" runat="server" Text="My Tooltip Text"></asp:Label>

</telerik:RadToolTip>

i need to bind the combo box to a linq datasouce and when clicked it show a 2 cols dropdown.

i keep getting error message on the e.Item.DataItem conversion what should the ????? be ?

Protected Sub RdProviders_ItemDataBound(ByVal sender As Object, ByVal e As RadComboBoxItemEventArgs)

Dim ds As New mobilesdcDataContext

e.Item.Text =

DirectCast(e.Item.DataItem, ?????)("ProviderExtension").ToString() + "; " + (DirectCast(e.Item.DataItem, ??????))("ProviderName").ToString()

e.Item.Value = (

DirectCast(e.Item.DataItem, ?????))("ProviderExtension").ToString()

End Sub

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

If Not Page.IsPostBack Then

Dim ds As New mobilesdcDataContext

Dim result = From p In ds.Providers_tbls Select p

rbProviders.DataSource = result.ToList

rbProviders.DataTextField =

"ProviderName"

rbProviders.DataValueField =

"ProviderExtension"

rbProviders.DataBind()

End If

End Sub